The present invention relates to a high frequency power amplifier module (or a high frequency power amplifier) including a plurality of amplification lines for linear amplifications and for non-linear amplifications (or saturated amplifications), and a wireless communication system packaging the high frequency power amplifier module.
More particularly, the invention relates to a technique effective when applied to a multi-mode communication type cellular mobile phone having a plurality of communication functions of different communication modes.
In North America, in recent years, there has been employed the so-called xe2x80x9cdual mode mobile phonexe2x80x9d in which there are incorporated into one mobile phone: the analog type AMPS (Advanced Mobile Phone Service) employed in the prior art and covering the entire North America; and the digital system such as the TDMA (Time Division Multiple Access) or the CDMA (Code Division Multiple Access).
In Europe and so on, on the other hand, there has been employed the GSM (Global system for Mobile Communication) system using the TDMA technique and the FDD (Frequency Division Duplex) technique. In the GSM system, on the other hand, there has been developed the EDGE (Enhanced Data Rates for GSM Evolution) system as the communication system capable of enhancing the transmission rate.
The multi-mode communications by the dual mode mobile phone or the like are described, for example, on pp. 115 to 126 of xe2x80x9cNIKKEI ELECTRONICSxe2x80x9d (No. 681), issued by NIKKEI BP on Jan. 27, 1997.
Into the wireless communication system (or the mobile phone), there is incorporated an amplifier (or the high frequency power amplifier module) packaging transistors in multiple stages. The communication system is seriously influenced by the performance of the high frequency power amplifier module.
In Japanese Patent Laid-Open No. 154321/1992, there is disclosed a high frequency power amplifier which can control the high frequency output power over a wide range while retaining the satisfactory linear characteristics and the power efficiency stably. This high frequency power amplifier has a multistage construction using a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or a GaAs-FET in the final stage circuit so that the high frequency output power is variably controlled by changing the bias condition of the drive circuit from the outside while keeping the bias of the final stage circuit constant. There is also disclosed a technique for controlling the output power by incorporating a variable attenuator circuit into a high frequency input line of the aforementioned circuit.
In Japanese Patent Laid-Open No. 26776/1999, on the other hand, there is disclosed a power amplifier which can reduce the power consumption without increasing the distortion and can improve the power efficiency. This power amplifier has a high frequency circuit employing a dual gate FET. This power amplifier is constructed such that two stages of dual gate FETs are cascade-connected between an input terminal In and an output terminal OUT. Specifically, the first gate on the drain side of the dual gate FET at the first stage is connected with the input terminal IN, and the drain is connected with the first gate on the drain side of the dual gate FET at the final stage. The drain of the dual gate FET at the final stage is connected with the output terminal OUT. The first gates of the first stage and the final stage are connected with a first gate input terminal G1, and the second gates of the first stage and the final stage are connected with a second gate input terminal G2.
Most wireless data communications, as used in the mobile communications, are effected at a transmission rate of 9.6 Kbps. Since a higher transmission speed has been demanded for accessing to the internets or data bases of enterprises, however, there has been needed a communication system for the high speed. The GSM system servicing mainly in Europe and Asia has the transmission rate of 9.6 Kbps at present. In order to satisfy the demands thus far described, however, there has been developed the EDGE system having the high transmission rate. By introducing this system, the data transmission rate is raised to as high as 48 Kbps so that data of four times as high as that of the GSM system can be transmitted for a unit of time.
Another advantage of the EDGE system is that it can be run without introducing any new infrastructure because it is practiced by using the basic system of the GSM with a partial change in the wireless modulation method. This little change is attractive for many communication businessmen.
For the modulation method, the GSM system adopts the GMSK (Gaussian Minimum Shift Keying) modulation, but the EDGE system adopts the 3xcfx80/8-rotating 8PSK (Phase Shift Keying) modulation. This means the change from the GMSK modulation method to the 3xcfx80/8-rotating 8PSK modulation method. For this change in the modulation method, the signal transmission unit of the wireless communication system is required to have a higher linearity.
Since the EDGE system is developed from the GSM system, one mobile phone can desirably communicate with the GSM system and the EDGE system. This makes it necessary to incorporate both an amplifier for the GSM system and an amplifier for the EDGE system in the mobile phone.
We have examined a high frequency power amplifier module which can cover both the GSM system and the EDGE system with one amplifier and have found out the following problems to be solved.
(1) The transistor acts, when employed in the GSM, in the saturated state so that a high power is demanded. For an input signal at about 0 dBm, as modulated in the GMSK, an output power required is about 36 dBm at the maximum.
(2) The transistor acts, when employed in the EDGE, in the linear state so that a linearity is demanded. For an input signal modulated at the 3xcfx80/8-rotating 8PSK, specifically, no distortion is required for the output signal. On the other hand, the maximum of the linear output power is within a range of about 28 to 29 dBm.
(3) Since the GSM system and the EDGE system have a large difference in the output power, as described above, it is questionable how to realize the two system with the single amplifier. Specifically, the system for making the non-linear action and the linear action compatible is exemplified by the AMPS (for the saturated action)/the CDMA (for the linear action) of North America. In this case, the maximum output power is about 30 to 32 dBm for the AMPS but about 28 to 29 dBm for the CDMA, so that the different is 2 to 3 dBm. Therefore, the compatible system is easily enabled to match the two actions by making the input power variable, even if it is operated at the same bias voltage. In the GSM/EDGE, however, the maximum power has a difference as large as 6 to 8 dBm so that the two system cannot be made compatible with one circuit.
(4) The mobile phone is powered by the battery so that it is required to a higher efficiency for a longer use. For example, the GSM is required to have an efficiency of about 50 to 60%, and the EDGE is required to have an efficiency of about 35 to 40%. This makes it desirable to make the used power amplification element as small as possible.
An object of the invention is to provide a high frequency power amplifier module and a wireless communication system for making the GSM system (for the saturated action) and the EDGE system (for the linear action) compatible in one circuit.
Another object of the invention is provide a high frequency power amplifier module and a wireless communication system, which can improve the AM modulation (or the AM-AM conversion).
Still another object of the invention is to provide a high frequency power amplifier module and a wireless communication system, which can easily isolate input and output terminals while causing little signal leakage.
The foregoing and other objects and novel features of the invention will become apparent from the description to be made with reference to the accompanying drawings.
The representative of the invention to be disclosed herein will be briefly summarized in the following.
(1) According to an aspect of the invention, there is provided a high frequency power amplifier module having a multistage amplifier construction, in which a plurality of semiconductor amplification elements are sequentially cascade-connected. The high frequency power amplifier module includes at least an input terminal, an output terminal, a control terminal and a mode switching terminal as its external terminals. The amplification element at the first stage is exemplified by a dual gate FET, which is fed at a first gate G1 close to its drain with a signal from the control terminal and at a second gate G2 with a radio signal from the input terminal. To the second gate G2, on the other hand, there is applied a bias voltage which is based on the signal from the control terminal and a signal from the mode switching terminal. In accordance with the signal from the mode switching terminal, the high frequency power amplifier module is caused to act as an amplifying line for the GSM or an amplifying line for the EDGE. In this case, the amplifying line for the GSM system acts non-linearly so that its output power is about 36 dBm at the maximum, and the amplifying line for the EDGE system acts linearly so that its output power is about 29 dBm at the maximum.
According to this means:
(a) the GSM system (for the saturated action) and the EDGE system (for the linear action) can be realized in the common circuit; and
(b) in the high frequency power amplifier module of the multistage amplifier construction, the input stage (or the first stage) is constructed to include a dual gate FET which is fed at its first gate with a control voltage. As seen from a graph of FIG. 3, therefore, the AM-AM conversion (AMout) can be improved to 16% or less for an input power Pin of 6 dBm or higher.